Replacement Problem Research Articles

Asset management strategies for wind turbines: keeping or retrofitting existing wind turbines

In this study, a parallel replacement problem with retrofitting (PRP-R) model is proposed to determine the trade-off between retrofitting and replacing an asset. The primary objective is to identify the replacement, maintenance and retrofitting schedule that optimise purchasing new assets, operation and maintenance (O&M) cost, and retrofitting cost under budget and production constraints resulting in a mixed-integer linear programming formulation. This model is applied to a case study of energy industry involving wind turbines (WTs). Results show that due to a lower O&M cost, retrofitting is less costly than keeping the WTs. In addition, the effects of key parameters such as O&M cost, retrofitting cost, budget allocated for retrofitting and governmental subsidy on the optimal replacement policy on total cost are studied. This research contributes a model that can be used to determine if WT retrofitting is economically justified and provides a rigorous analytical framework for optimising the decision-making process over the wind farm life cycle.

Strategic vehicle fleet management–a joint solution of make-or-buy, composition and replacement problems

PurposeThe purpose of this paper is to develop an original model and a solution procedure for solving jointly three main strategic fleet management problems (fleet composition, replacement and make-or-buy), taking into account interdependencies between them.Design/methodology/approachThe three main strategic fleet management problems were analyzed in detail to identify interdependencies between them, mathematically modeled in terms of integer nonlinear programing (INLP) and solved using evolutionary based method of a solver compatible with a spreadsheet.FindingsThere are no optimization methods combining the analyzed problems, but it is possible to mathematically model them jointly and solve together using a solver compatible with a spreadsheet obtaining a solution/fleet management strategy answering the questions: Keep currently exploited vehicles in a fleet or remove them? If keep, how often to replace them? If remove then when? How many perspective/new vehicles, of what types, brand new or used ones and when should be put into a fleet? The relatively large scale instance of problem (50 vehicles) was solved based on a real-life data. The obtained results occurred to be better/cheaper by 10% than the two reference solutions – random and do-nothing ones.Originality/valueThe methodology of developing optimal fleet management strategy by solving jointly three main strategic fleet management problems is proposed allowing for the reduction of the fleet exploitation costs by adjusting fleet size, types of exploited vehicles and their exploitation periods.

Optimal replacement strategies for warranty products with multiple failure modes after warranty expiry

The optimal replacement problem for a warranty product subject to (M + 1) types of mutually exclusive failure modes, including M repairable failure modes and a catastrophic failure mode, is investigated in this paper. When the product fails with a repairable failure mode, a minimal repair will be conducted to remove the failure. However, if a catastrophic failure mode occurs, the failure product can only be replaced by a new one. Within the warranty period, the seller needs to complete each failure repair within a repair time limit. Once a failure cannot be repaired within the stipulated time, under the rebate warranty, the customer is refunded a proportion of the sale price of the product based on its working time, and the warranty terminates simultaneously; or under the free replacement warranty, the seller is obligated to provide a new product at no charge to the customer. Under both the warranty policies, the repair cost is free of charge to the customer within the warranty time, while the customer is responsible for all the cost for repairs within the post-warranty time. From the customer’s point of view, the expected life cycle cost rate of the product under the rebate and free replacement warranty are respectively derived. The existence and uniqueness of the optimal replacement strategies after warranty expiring are also proved theoretically by minimizing the cost rate. Finally, we give numerical examples to illustrate the two warranty models and show the effectiveness of proposed strategies.

Design and optimization of low-temperature gradient thermoelectric harvester for wireless sensor network node on water pipelines

Low-temperature gradients between massive solids and ambient air are ubiquitous due to a diurnal temperature cycle. The use of these gradients as a source of renewable energy to power the low power-consuming nodes of a wireless sensor network instead of batteries can solve the problem of periodic replacement of batteries with their subsequent recycling. This study successively presents the stages of modeling, development, optimization, assembling, and experimental validation of a thermoelectric harvester for replacement of a 20 Ah battery for a wireless water quality sensor located on a water pipe. The experiments confirmed that the thermoelectric harvester produces more than 0.5–2mW at a temperature difference of about 1–2 K between the pipe surface and the surrounding air at the calm wind speed of about 1 m/s. The original dimensionless model of thermoelectric harvester is presented herein. The key role of convective heat transfer in the harvesting process is demonstrated.

The New Normal?

The article discusses the preliminary results of the forced transition to entire online learning in the higher education system in the context of the general growth trend of the corresponding form of education in various universities around the world. The ideology defining this trend is considered. Special attention is paid to the analysis of the reality of a sharp increase in the level of control of both teachers and students by the creators of training platforms, as well as the possible consequences of this situation. It is shown that universities in different countries are seeking suitable forms of supplementing regular education with remote ones. The overall trend is a steady growth in online learning with significant variations across countries (examples include the United States, Australia, Germany, and China). It is obvious that national education systems differ significantly from each other, and with certain general trend towards online learning, each educational system is looking for its own, most suitable for the national culture, forms of education. It is also necessary to understand how online learning can be integrated into existing system without harm. At the moment, this is not clear either on the content level or methodological one. The article analyzes the temporary and long-term problems associated with the transition to distant education. The problem of technical support is probably the easiest to be solved. More serious and requiring new technologies is the problem of changing the nature of communication, which requires quite different efforts of both teachers and students if compare with the usual ones. Working on the platforms that are intended to radically change the educational environment under the slogans of ensuring an individual educational trajectory, in fact leads to the opposite. The author dwells on the problem of possible widespread replacement of conventional courses with recorded ones and, especially, the ideology of transition to online learning in the format of virtual reality, which allows the creators to exercise full control over the individual. The problem of monitoring of educational activities is discussed, which already in the current conditions makes it possible to record any actions and states of all participants in the process. The article is a reaction to the beginning of the process of widespread introduction of online technologies, and this approach, according to the author, allows to observe vividly the most painful aspects of the new situation (like the first impression of a meeting with the unknown).

Estimation of the effects of inset heights and slit configurations in an acetabular cup on the pull-out behavior of an artificial hip joint with a structure for preventing dislocation using finite element analysis.

Joint dislocation is a critical problem of total hip replacement. We have newly proposed an artificial hip joint with a structure that prevents dislocation. The proposed joint has a simple form with a femoral head partially covered with an acetabular cup. In the present study, the effects of inset heights and slit configurations of the cup on the pull-out forces of the joint were evaluated using finite element analysis. Joint models with different inset heights and those with or without a slit in the cup were used for the analyses to estimate the pull-out forces of the joint. In the case without the slit, the maximum pull-out force of the joint with 1.0 and 1.5mm of the inset height was approximately 12 and 40N, respectively. In the case of 1.0-mm inset height, the maximum force of the joint with and without the slit was approximately 9 and 12N, respectively. These results reveal that the maximum force is markedly changed by the inset height and is moderately affected by the slit. Thus, we can gain insights into a strategy to optimally design an artificial joint in which dislocation does not occur easily. Graphical abstract.

The Performance of Cemented Femoral Prosthesis Based on New Gel Materials

In view of the problems in hip replacement, a new gel material is developed and incorporated into cemented femoral prosthesis. The material precipitates hydroxyapatite (HA) onto silk fibroin (SF) by biomimetic method, namely silk fibroin hydroxyapatite (SF–HA). Through X-ray diffraction (XRD) and scanning electron microscope (SEM) analysis, HA precipitates on SF. Taking the gel time as the standard, 5 groups of gel materials are selected. Through in vitro degradation experiments, the degradation rate of these materials is 45%∼55%. Cell experiments (mouse L929 cells, osteoblasts HO-F) show that these cells have no cytotoxicity and support the growth of osteoblasts. In addition, in the vivo experiment (two groups), one group was treated with gelatin materials and the other group is treated with bone cement prosthesis transplantation directly. Comparing the indexes before and after operation, it proves that the new gel material has great application value in hip replacement surgery.

Fuzzy environment replacement model

This paper focuses on replacement of equipment in fuzzy environment. Fuzzy set theory is the main tool to emphatic the vagueness parameters which involving in many real life applications. All imprecise costs involved in this fuzzy replacement model are taken as triangular fuzzy numbers. The proposed method gives the optimal replacement time of the replacement problem in fuzzy nature and it is validated using a real life numerical example.

Research on hydraulic permeability enhancement technology of high, medium and low pressure coal seam with deep well and high ground stress

Aiming at the problem of poor gas extraction, long outburst time and low pre-drainage efficiency in the drilling zone of the floor tunnel through the drilling, the problem of mining excavation replacement is severely restricted. Dingji Coal Mine has carried out ultra-high pressure, medium pressure, and low pressure hydraulic cutting coal seam enhanced permeability gas extraction technology tests. Through continuous exploration and summary, it has achieved remarkable results, maximized extraction, and accumulated rich hydraulic coal Through experience. The results show that: the high-pressure hydraulic coal seam anti-reflection pre-draining unit has a maximum extraction pure volume of 3.1m3/min, the single-hole average extraction pure volume is 0.008m3/min; the medium-pressure hydraulic coal seam anti-reflection pre-extraction unit has a maximum extraction pure volume of 2.2 m3/min, single-hole average extraction pure volume is 0.005m3/min; low-pressure hydraulic coal seam permeability enhancement unit extraction pure volume is maximum 1.3m3/min, single-hole average extraction pure volume is 0.002m3/min. 1351(1)Yunshun’s gas pre-drainage rate reached 65.2% after adopting high-pressure hydraulic coal seam penetration enhancement measures. Through statistical analysis of the anti-burst prediction index during coal tunnel footage, the sensitive index is relatively small, and the effect of pre-draining outburst is better. The lane enters 200m per month. The permeability enhancement technology of hydraulic coal seam has a significant effect on the pre-drainage of gas in high ground pressure outburst coal seam. It provides an effective method for improving the gas pre-drainage and outburst work, which is worthy of in-depth promotion and application.

Ensuring consistency between strategic plans and equipment replacement decisions

ABSTRACT Strategic business plans are based upon assumptions of future wood costs. Future wood costs are affected by future equipment cost inputs and technological change. Equipment replacement decisions react to future cost inputs and technological change, taking advantage of opportunities to reduce future wood costs. By explicitly defining future equipment cost inputs and technological change, and their effect on equipment replacement decisions, future wood costs used in strategic planning have a rational and consistent basis. To ensure consistency between strategic plans and equipment replacement decisions we developed a forward reaching dynamic programming algorithm that recognizes the special structure of the equipment replacement problem. The output is an equipment replacement schedule that can be used to project equipment investment needs, operational costs, and tree harvesting costs. The results show that when we compare the proposed algorithm with the classic infinite series machine replacement approach under constant costs, both of them presented an optimal life with 52 months and a discounted cost of 5.691 USD million. Considering a 1200 month planning horizon under technological changes, the economic life policy proved optimum with 80 months of use for the first machine, while the next generations varied between 69 and 71 months of use with a discounted cost value of 4.617 USD million. Under the estimates of future costs and technological improvements, production costs decline and production rises. The algorithm is intuitive, flexible, easy to calculate, and yields the exact solution. No restrictions are needed on cost inputs over time, technologies, or discount rates.

Design and Analysis of Porous Functionally Graded Femoral Prostheses with Improved Stress Shielding

One of the most important problems of total hip replacement is aseptic loosening of the femoral component, which is related to the changes of the stress distribution pattern after implantation of the prosthesis. Stress shielding of the femur is recognized as a primary factor in aseptic loosening of hip replacements. Utilizing different materials is one of the ordinary solutions for that problem, but using functionally graded materials (FGMs) could be better than the conventional solutions. This research work aims at investigating different porous FGM implants and a real femoral bone by a 3D finite element method. The results show that a neutral functionally graded prosthesis cannot extraordinarily make changes in the stress pattern of bone and prosthesis, but an increasing functionally graded prosthesis leads a lower level of stress in the prosthesis, and a decreasing functionally graded prosthesis can properly reduce the stress shielding among these three architectures. Due to the absence of similar results in the specialized literature, this paper is likely to fill a gap in the state-of-the-art bio-implants, and provide pertinent results that are instrumental in the design of porous femoral prostheses under normal walking loading conditions.

Popularity-Based and Version-Aware Caching Scheme at Edge Servers for Multi-Version VoD Systems

Recently, many video-on-demand (VoD) providers have begun storing multiple versions of the same video to offer multiple-quality video services with different bitrates to users, called multi-version VoD. To improve users’ quality of experience (QoE), it is a good idea to cache videos at edge servers in multi-version VoD systems. However, determining which versions of which videos should be cached or replaced in an edge server is still a major challenge for a multi-version VoD system because of its limited cache storage. In this paper, we propose a popularity-based and version-aware caching scheme (PVCS) at edge servers for multi-version VoD systems. First, based on video popularity, we formulate cache placement as a knapsack problem under constraints such as the cache storage and transcoding computation of the edge server, which aims to maximize the cache hit ratio. Second, we use the transcoding relations among versions to calculate a version-aware caching profit when caching a certain version or multiple versions of a video. The version-aware caching profit is the basis for the subsequent cache replacement algorithm. Third, we propose two algorithms, the video cache placement (VCP) algorithm and the video cache replacement (VCrP) algorithm, to solve the cache placement and replacement problems respectively. VCP utilizes the Lagrangian relaxation algorithm to decide which video files should be cached initially, and VCrP decides which video files cached at the edge server will be replaced dynamically based on the version-aware profit. In this way, the PVCS can improve the cache hit ratio and decrease the average start-up delay. Our simulation results have shown that the PVCS outperforms the other schemes in terms of the cache hit ratio and the average start-up delay.

A comprehensive review on dual approach to the vibration analysis: Some dual techniques and application

This paper reviews key ideas of the researches on the dual approach to the vibration analysis. Three types of dual techniques, namely, forward - return dual technique, global-local dual technique, weighted averaging dual technique for the problem of equivalent replacement are summarized. Different implements and realizations of dual techniques to nonlinear vibration analysis and design of dynamic absorbers are reviewed. Finally, the challenging issues based on the dual techniques are discussed. A number of possibilities for developing analytical techniques related to dual techniques are proposed. The review shows that the dual approach is an appropriate one and the dual techniques are effective tools for studying random and deterministic nonlinear vibrational systems.

Optimal asset replacement: Profit maximization under varying technology

The paper analyzes a profit-maximizing serial replacement problem under variable asset productivity, operating cost, and replacement cost that depend on asset age and installation time. The majority of modern asset replacement models minimize costs. The authors examine and highlight essential differences between profit-maximizing and cost-minimizing replacement strategies in the infinite-horizon framework. Next, they construct and analyze an effective multi-cycle replacement algorithm that approximates the infinite-horizon solution with non-equal asset lifetimes. Numeric simulation illustrates theoretic outcomes and demonstrates a good performance of the constructed algorithm under different patterns of changing technology.

Non-equal-life asset replacement under evolving technology: A multi-cycle approach

This paper studies the cost-minimizing serial asset replacement problem under changing operating and replacement costs. Technological improvements affect these costs in different ways, which leads to different duration of sequential replacement cycles of the same asset. Therefore, a firm should optimize a chain of consecutive asset replacements using available information about future costs. We offer a novel multi-cycle algorithm for making such replacement decisions and prove that it converges to the infinite-horizon solution when the number of cycles increases. Important qualitative properties of the obtained optimal non-equal-life replacement strategies are derived, and practical recommendations are discussed.

Nash equilibrium based replacement of virtual machines for efficient utilization of cloud data centers

Workload uncertainty has been increased with the integration of the Internet of Things to the computing grid i.e. edge computing and cloud data centers. Therefore, efficient resource utilization in cloud data centers become more challenging. Dynamic consolidation of virtual machines on optimal number of processing machines can increase the efficiency of resource utilization in cloud data centers. This process requires the migration of virtual machines from the under-utilized and over-utilized processing machines to other suitable machines. In this work, the problem of efficient replacement of virtual machines is solved using a game theory based well known technique, Nash Equilibrium (NE). We designed a nash equilibrium based dual on two players, over-load manager and under-load manager, to deduce the dominant strategy profiles for various scenarios during consolidation cycles. Dominant strategy profile is the set of strategies where every player has no incentive in deviation, thus leading to equilibrium position. A virtual machines redeployment algorithm, Nash Equilibrium based Virtual Machines Replacement (NE-VMR), has been proposed on the basis of the dominant strategy profiles for efficient consolidation. Experiment results show that NE-VMR is a more efficient server consolidation technique, saved 30% energy and improved 35% quality of service as compared to baselines.

ПОРІВНЯННЯ АЛЬТЕРНАТИВНИХ СТРАТЕГІЙ ПОЕТАПНОЇ ЗАМІНИ ОБЛАДНАННЯ: СПЕЦІАЛЬНІ ВИПАДКИ

У даній роботі розглянуті спеціальні випадки, що виникають при ров’язанні задачі поетапної заміни обладнання, яким не приділено увагу в роботах, присвячених методам її розв’язання. Вона є продовженням дослідження, проведеного в [8]. При ров’язанні поставленої задачі методом динамічного програмування іноді виникає ситуація, коли в зоні заміни знаходяться елементи, для яких більш доцільним є збереження обладнання. Можливі декілька шляхів подолання даної проблеми. Деякі з них розглянуті в [8]. Дане дослідження передбачає розширення планового періоду, що дозволяє розглянути і порівняти альтернативні стратегії оновлення. Збільшення планового періоду дозволяє розглянути можливість збереження обладнання більшого віку, якщо це приносить більший прибуток, ніж його заміна. З іншого боку зменшується ступінь довіри до показників в останніх інтервалах цього періоду, що пов'язано зі зміною кон'юнктури ринку і зменшенням достовірності довгострокових прогнозів. Застосування різних способів усунення зазначеної вище проблеми продемонстровано на абстрактному прикладі. Проведено порівняння різних стратегій оновлення, що базуються на аналізі розподілу прибутків по роках планового періоду. Розглянуто також розподіл інвестицій по роках, що істотно впливає на вибір оптимальної стратегії відновлення. Акцентовано увагу на тому, що особа, яка приймає рішення, більш схильна до вибору стратегій, які приносять більший прибуток в початкові інтервали планового періоду і вимагають більш рівномірного розподілу інвестицій. Даний приклад для простоти передбачає рівномірний розподіл обладнання за віком на початку планового періоду. Однак, наведені формули для розрахунку прибутків і інвестицій є універсальними і можуть бути використані в будь-яких практичних розрахунках. На завершення слід зазначити, що найбільш ефективними, описані підходи є при виборі оптимальних стратегій оновлення обладнання з невеликим терміном морального зношуванння. При цьому інтервал (крок) планового періоду може дорівнювати не року, а кварталу або навіть місяцю.

The problem of the actual replacement of private property rights by rights of use in Ukraine: status and prospects

The article has substantiated the process of the de facto replacement of the right of private property by the rights of use; distinguished stages in the development of the private property institution in Ukraine; specified grounds for the emergence and termination of the right of private property and the rights of use; refined sense and scope of responsibility of the private owner and the holder;identified the main instrument of substitution of the right of private property by the rights of use; traced preconditions for passing inconsistent judgements on property protection by the ECHR; and analyzed possible consequences of further substitution of the right of private property by the rights of use. Regard to findings of the study it was considered about instability of the private property institution; identity between unofficial grounds for the termination of the right of private property and unofficial grounds for the emergence of the rights of use; existence of the direct threat to owner status in Ukraine; absence of legal grounds for increasing the sense of owner responsibility, including taxation of the private property; transformation of the feudal law into the modern rights of use combined with the right of possession; possibility of establishing a real type of polity and prospects for its development by ways of regulation of the ownership relations. The article has also considered about creating preconditions for restoring the feudal law and replacing democratic polity by a monarchy in Ukraine and other countries owing to severe restrictions on the right of private property, above all, through taxation of the privateproperty, and its de facto replacementby the rights of use.

Valuing tradeability in exponential Lévy models

The present article provides a novel theoretical way to evaluate tradeability in markets of ordinary exponential Levy type. We consider non-tradeability as a particular type of market illiquidity and investigate its impact on the price of the assets. Starting from an adaption of the continuous-time optional asset replacement problem initiated by McDonald and Siegel (1986), we derive tradeability premiums and subsequently characterize them in terms of free-boundary problems. This provides a simple way to compute non-tradeability values, e.g. by means of standard numerical techniques, and, in particular, to express the price of a non-tradeable asset as a percentage of the price of a tradeable equivalent. Our approach is illustrated via numerical examples where we discuss various properties of the tradeability premiums.

Dynamic Caching Content Replacement in Base Station Assisted Wireless D2D Caching Networks

The concentrated popularity distribution of video files and the caching of popular files on users and their subsequent distribution via device-to-device (D2D) communications have dramatically increased the throughput of wireless video networks. However, since popularity distribution is not time-invariant, and the files available in the neighborhood can change when other users move into and out of the neighborhood, there is a need for replacement of cache content. In this work, we propose a practical and feasible replacement architecture for base station (BS) assisted wireless D2D caching networks by exploiting the broadcasting of the BS. Based on the proposed architecture, we formulate a caching content replacement problem, with the goal of maximizing the time-average service rate under the cost constraint and queue stability. We combine the reward-to-go concept and the drift-plus-penalty methodology to develop a solution framework for the problem at hand. To realize the solution framework, two algorithms are proposed. The first algorithm is simple, but exploits only the historical record. The second algorithm can exploit both the historical record and future information, but is complex. Our simulation results indicate that when dynamics exist, the systems exploiting the proposed designs can outperform the systems using a static policy.